The present invention relates to a process for the conversion of pentamethylenetetramine derivatives into the corresponding tetrazocine derivatives. More particularly, the present invention is directed to a process for selectively cleaving the bicyclononane system to form tetrazocine derivatives, which derivatives preferably have two N-NO.sub.2 functions. Examples of the tetrazocine derivatives prepared in accordance with the present invention include, among others, 1,5-diacetyl-3,7-dinitrooctahydrotetrazocine (prepared by selectively cleaving 1,5-diacetyl-1,3,5,7-tetraazabicyclo[3.3.1]nonane); 1,5-disulfonyl-3,7-dinitrooctahydrotetrazocine (prepared by selectively cleaving 1,5-disulfonyl-1,3,5,7-tetraazabicyclo[3.3.1]nonane); 1,5-dibenzoyl-3,7-dinitrooctahydrotetrazocine (prepared by selectively cleaving 1,5-dibenzoyl-1,3,5,7-tetraazabicyclo[3.3.1]nonane); and 1,5-di(trichloroacetyl)-3,7-dinitrooctahydrotetrazocine (prepared by selectively cleaving 3,7-di(trichloroacetyl)-1,3,5,7-tetraazabicyclo[3.3.1]nonane). The above tetrazocine derivatives are effective intermediates for the preparation of 1,3,5,7-tetranitrooctahydrotetrazocine, hereinafter referred to as HMX, which is a high melting explosive of great commercial value.
All of the presently known and used methods of manufacturing HMX were developed during World War II. These methods employ hexamethylenetetramine as the starting material. Nitrolysis of this compound produces mixtures of the six-membered ring compound cyclotrimethylenetrinitramine, hereinafter referred to as RDX, and HMX, together with minor amounts of other open chain products. Existing methods produce large amounts of RDX (a valuable explosive) with HMX being obtained in only very small yields. There is an ever-increasing interest in producing HMX as the sole product from such nitrolysis reactions so that the expensive procedures required to separate HMX from RDX can be avoided. In addition, the cost of production should be competitive with presently available methods.
In the synthesis of HMX preferentially from hexamethylenetetramine, the key step is the selective cleavage of the bridgbon between the 1- and 5-positions. The most efficient way to obtain the eight-membered HMX compound is to convert hexamine (hexamethylenetetramine) into the tetraazabicyclo(3,3,1)nonane system and then to selectively cleave the bridge methylene to produce the eight-membered ring. This method would have obvious advantages over any attempts to synthesize HMX directly from other simpler building blocks due to the well-known reluctance of open chain compounds to form rings larger than six-membered rings.
Accordingly, an object of the present invention is to provide an improved process by which a pentamethylenetetramine derivative can be converted into the corresponding tetrazocine derivative.
Another object of the present invention is to provide an improved process for the preparation of tetrazocine derivatives which are effective intermediates in the subsequent preparation of the explosive HMX.
A further object of the present invention is to produce HMX by converting a bicyclononane system into an eight-membered structure and then converting said structure into HMX.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Pursuant to the present invention, it has been found that the above-mentioned disadvantages may be eliminated and a much improved method for producing particular tetrazocine derivatives as intermediates for the subsequent preparation of the explosive HMX can be obtained by nitrolyzing a pentamethylenetetramine derivative into the corresponding dinitro-diacyl, dinitro-disulfonyl, dinitro-di(trichloroacetyl), dinitro-dibenzoyl, dinitro-dinitroso, or other such octahydrotetrazocine compound. Thus, the present invention is concerned with an improved method for producing 1,5-diacetyl-3,7-dinitrooctahydrotetrazocine, hereinafter referred to as DADNT, in high yields and substantially free from other compounds by nitrolyzing a tetraazabicyclo(3,3,1)-nonane derivative, that is, 1,5-diacetyl-1,3,5,7-tetraazabicyclo-(3,3,1)nonane, hereinafter referred to as DAPT or diacrtylpentamethylenetetramine. The method is concerned also with producing related octahydrotetrazocine compounds such as 1,5-dinitroso-3,7-dinitrooctahydrotetrazocine by nitrolyzing 1,5-dinitroso-3,7-tetraazabicyclo[3.3.1]nonane, hereinafter referred to as DNPT or dinitrosopentamethylenetetramine. Still other octahydrotetrazocine compounds produced in accordance with the present invention include 1,5-disulfonyl-3,7-dinitrooctahydrotetrazocine; 1,5-di-(trichloroacetyl)-3,7-dinitrooctahydrotetrazocine; 1,5-dibenzoyl-3,7-dinitrooctahydrotetrazocine and the like.
The present process produces a yield as high as about 75% of the above tetrazocine derivatives. Moreover, the tetrazocine derivatives are substantially free from other compounds, such as RDX, and have a high level of purity which makes them readily convertible to HMX without any further purification being required. The present process eliminates the prior art problems of forming large amounts of the six-membered ring products and open chain products by producing in high yield a water insoluble, readily isolatable, eight-membered ring product which already has two N-NO.sub.2 functions. Furthermore, no other side products are formed in the reaction.
The pentamethylenetetramine derivatives, for example, DNPT or DAPT are nitrolyzed by reacting them with dinitrogen tetroxide, fuming nitric acid, nitric acid or an inorganic nitrate, for example the alkali metal nitrates. Suitable alkali metal nitrates include sodium nitrate or potassium nitrate or mixtures thereof. Advantageously, the nitric acid or inorganic nitrates are mixed with concentrated sulfuric acid and then said solution is added to the pentamethylenetetramine derivative. The addition of said reagents effects the selective cleavage of the bicyclononane system to the tetrazocine derivative.
The present process, unlike the other prior art methods, requires neither cooling nor heating of the reaction mixture either during the addition or during the aging steps of the process and thus the present process can be conducted at ambient temperatures. This, of course, results in a considerable financial savings when the tetrazocine derivative of the present invention is produced on a commercial scale.
The resulting product, for example, 1,5-diacetyl-3,7-dinitrooctahydrotetrazocine can be subsequently converted into the explosive HMX by reacting it with concentrated nitric acid, for example, 99% nitric acid at room temperature. The high yield of DAPT from hexamine (about 99%) makes the present process a valuable method in the production of HMX, completely free of RDX and other open chain derivatives. As a matter of fact, the present invention provides for the non-isolation or purification of the intermediate DADNT in its further conversion to HMX.
The following examples are given merely as being illustrative of the present invention and are not to be considered as limiting.